Head-up display units (HUDs) and helmet-mounted display units (HMDs) display information in a user's field of vision without requiring the user to move his or her head. They are of particular use in safety-critical environments, for example in military aircraft cock-pits where it is desirable that the aircrew, and especially the pilot(s), are provided with flight-critical information without having to look at instruments or otherwise divert their line of sight from an external scene. As a display enhances or supplements the user's view of an external world scene, an important feature is that most of the display is see-through, so that the world view is not unduly obscured. The skilled person will be familiar with the type of avionic information and symbology typically included in images for display by HUDs and HMDs when used by aircraft pilots, for example. As such displays provide real-time information and symbology, image updates need to be generated for display at a high rate and with low latency.
Typically, image generators use a graphics processor unit (GPU) for image generation. While able to provide good performance, GPUs can be power-hungry, difficult to certify to the required design assurance level (DAL) and have a short lifespan as compared to typical avionic product life times of 25 or more years. This may result in obsolescence replacement programs, and expensive re-certification of the avionics following a design change.
An implementation for an image generator is therefore required that combines relative ease of certification to the required standards with a required level of performance defined in terms of overall latency of an associated display system from receipt of data to be displayed to visibility of updated imagery on the display device. One contributing element to the overall latency of the display system is the time required to render images defined in drawing commands received by the image generator. The present invention addresses the latter aspect.